1. Field of the Invention
The present invention relates to printer apparatus and, more particularly, to a line feed mechanism therefor.
2. Description of the Prior Art
There have been a number of different types of automated line feed mechanisms proposed and/or employed heretofore to periodically rotate a typewriter or a printer platen and, thereby, through frictional (or sprocket wheel) contact with a worksheet (or roll of paper) advance the latter either one or a limited pre-set number of line spaces periodically, normally dependent on each return of the carriage to its "home" position. Such mechanisms, for example, have often employed a cam-actuated pawl and ratchet wheel assembly, which has relied on the inertia produced by either a spring or a power returned carriage, to effect incremental single up to triple print line rotation of the platen.
In still other prior line feed mechanisms, a laterally movable stop or detent, often supported on a reciprocally driven carriage, has been employed to trip or otherwise actuate either associated mechanical or electromechanical apparatus which, in turn, effects line feed rotation of the platen. In the latter case, the platen has generally been rotated by the use of either an actuated pawl-ratchet wheel assembly, or by an operable clutch that incorporates an axially displaceable and rotatably driven member.
In all of such prior line feed mechanisms, line feeding is obviously only initiated when the carriage passes or arrives at a given point along its path of travel, and even then, usually from only a given direction. Such a point of carriage initiated platen rotation is typically located at or near the first print column position of the printer. It is thus seen that many line feed mechanisms employed heretofore have not provided selectively controlled, multiple line feeding versatility, i.e., where a number of print line advancements of a print medium much greater than two or three, for example, may be selectively produced, even when dependent on a return of a carriage to its "home" or some other preselected position.
This deficiency in line feed versatility has been particularly evident in high speed printers of the dot matrix type. In such printers, a carriage mounted print head is either stepped or continuously driven at a relatively rapid rate from one side of the platen to the other during the printing of a given line and, thereafter, generally driven even more rapidly to its starting or "home" position to commence the printing of the next line of information. Because of the speed of such printers, they are often used as peripheral equipment in computer systems, or as part of terminal station apparatus and, hence, are often involved in printing applications where very rapid multiple line feeding would be a great advantage, such as in formating, vertical tabulating or editing operations.
Even if prior line feed mechanisms were modified in some way to effect variable multiple line feeding, another problem that would normally exist is the noise (or clatter) that would be generated by the ratchet-detent mechanism necessarily employed to accurately and firmly hold the platen (and paper) during the printing of each line. Such noise can become very pronounced and objectionable in high speed printers, such as of the dot matrix type. By reason of the nature and manner in which most prior line feed mechanisms operate, to also selectively bias the detent in question out of engagement with the ratchet wheel during multiple line feeding would normally require separate poweroperated apparatus, such as an operably coupled solenoid, which would not only increase the cost and space requirements of, but the power consumed by, the composite line feed mechanism.
An additional problem that would be encountered in any attempt to modify most prior line feed mechanisms for more versatile, automated single and multiple line feeding applications, is the fact that such apparatus in its present form has tended to be rather complex mechanically, expensive and bulky. Such apparatus therefore does not readily lend itself to further modification and/or the incorporation of additional apparatus to effect selectively controlled and quiet multiple line feeding, and still readily be accommodated within the very close fitting housings of most high speed printers today. Such compactness, of course, is attributable in large measure to the utilization of solid state logic circuitry to control the printing operations. It, of course, is recognized that optimum line feed versatility could be achieved by utilizing a separate stepping motor to selectively rotate the platen of a printer independently of the power driven carriage. The cost of an additional stepping motor, as well as the space requirements therefor, however, would normally rule out that solution to line feeding in the highly competative field of high speed, low cost and compact carriage driven printers.